U.S. patent application number 15/297324 was filed with the patent office on 2018-04-19 for current sense element for current regulated circuit and the like and method therefor.
This patent application is currently assigned to SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC. The applicant listed for this patent is SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC. Invention is credited to Jean-Paul EGGERMONT.
Application Number | 20180109187 15/297324 |
Document ID | / |
Family ID | 60662052 |
Filed Date | 2018-04-19 |
United States Patent
Application |
20180109187 |
Kind Code |
A1 |
EGGERMONT; Jean-Paul |
April 19, 2018 |
CURRENT SENSE ELEMENT FOR CURRENT REGULATED CIRCUIT AND THE LIKE
AND METHOD THEREFOR
Abstract
In one form, a circuit having a current sense element includes a
current sense element, a target signal generator, and an error
signal generator. The current sense element has first and second
terminals and is adapted to be coupled in a current path whose
current is to be sensed. The target signal generator generates a
target signal representative of a condition of the current sense
element when the current sense element conducts a target current.
The error signal generator has an output for providing an error
signal in response to both a current flowing through the current
sense element and the target signal. In another form, a current
regulated circuit includes a current conducting element such as a
solenoid and a current control element coupled in series with the
current conducting element and the current sense element.
Inventors: |
EGGERMONT; Jean-Paul;
(Pellaines, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC |
Phoenix |
AZ |
US |
|
|
Assignee: |
SEMICONDUCTOR COMPONENTS
INDUSTRIES, LLC
Phoenix
AZ
|
Family ID: |
60662052 |
Appl. No.: |
15/297324 |
Filed: |
October 19, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 19/0092 20130101;
G05F 1/56 20130101; G01R 19/08 20130101; H02M 2001/0009 20130101;
H02M 1/08 20130101; H02M 3/158 20130101; G01R 31/34 20130101 |
International
Class: |
H02M 3/158 20060101
H02M003/158; H02M 1/08 20060101 H02M001/08; G01R 31/34 20060101
G01R031/34; G01R 19/08 20060101 G01R019/08 |
Claims
1. A circuit having a current sensor, the current sensor
comprising: a current sensing element having first and second
terminals and adapted to be coupled in a current path whose current
is to be sensed; a target signal generator for generating a target
signal representative of a condition of said current sensing
element when said current sensing element conducts a target
current; and an error signal generator having an output for
providing an error signal in response to both a current flowing
through said current sensing element and said target signal.
2. The circuit of claim 1, wherein said current sensing element
comprises: a sense resistor.
3. The circuit of claim 1, wherein said current sensing element
comprises: a current conduction element of a sense transistor.
4. The circuit of claim 3, wherein said target signal generator
comprises: a drain sense element of said sense transistor.
5. The circuit of claim 3, wherein said sense transistor is a
epitaxially fabricated metal-oxide-semiconductor (MOS) transistor
having a bulk terminal and a source wherein said bulk terminal is
isolated from said source.
6. The circuit of claim 1, wherein said target signal generator
generates a target voltage representative of a voltage drop across
said current sensing element when said current sensing element
conducts said target current.
7. The circuit of claim 6, wherein: said target signal generator
has first terminal coupled to one of said first and second
terminals of said current sensing element, a second terminal for
receiving a reference voltage, and a third terminal for providing
said target signal.
8. The circuit of claim 7, wherein said target signal generator
comprises: a current source having a first terminal for receiving a
reference voltage, and a second terminal for providing a target
current; and a matched resistor having a first terminal coupled to
said second terminal of said current source, and a second terminal
coupled to a corresponding one of said first and second terminals
of said current sensing element, wherein said matched resistor has
a resistance that is matched to a resistance of said current
sensing element.
9. The circuit of claim 8, wherein said matched resistor comprises:
a segmented resistor ladder having a plurality of resistive
segments coupled in series between said second terminal of said
current source and said second terminal of said current sensing
element; and a multiplexer having inputs coupled to terminals of
respective ones of said plurality of resistive segments, an output
for providing the target signal, and a control terminal for
receiving a control signal.
10. The circuit of claim 8, wherein said current source comprises:
a digital-to-analog converter having a first terminal for receiving
a reference current, a second terminal for receiving an input code,
and an output terminal for providing said target current.
11. The circuit of claim 6, wherein said target signal generator
comprises: a digital-to-analog converter having a first terminal
for receiving a reference voltage, a second terminal for receiving
an input code, a third terminal coupled to current sensing element,
and an output terminal for providing said target voltage.
12. The circuit of claim 1, wherein said error signal generator
comprises: a difference amplifier having a first input coupled to a
first terminal of said current sensing element, a second input for
receiving said target signal, and an output; and an
analog-to-digital converter having an input coupled to said output
of said difference amplifier, and an output for providing said
error signal as a digital error signal.
13. The circuit of claim 1, wherein said error signal generator
comprises: a difference amplifier having a first input coupled to a
first terminal of said current sensing element, a second input for
receiving said target signal, and an output; and a transistor
having a first current electrode coupled to one of said first and
second inputs of said difference amplifier, a control electrode
coupled to said output of said difference amplifier, and an output
for providing said error signal as an error current.
14. The circuit of claim 1, wherein the circuit is a current
regulated circuit further comprising: a current conducting element
having a first terminal coupled to a first power supply voltage
terminal, and a second terminal coupled to a first terminal of said
current sensor; a current control element having a first terminal
coupled to a second terminal of said current conducting element, a
control electrode, and a second current electrode coupled to a
second power supply voltage terminal; and a control circuit having
an input coupled to said output of said error signal generator, and
an output for providing a control signal to said control electrode
of said current control element, wherein said control circuit
changes said control signal to reduce said error signal.
15. The current regulated circuit of claim 14, wherein said control
circuit is coupled to said error signal generator through a
converter that converts said error signal into a digital error
signal.
16. The current regulated circuit of claim 14 wherein said current
conducting element comprises a solenoid.
17. A current regulated circuit comprising: a current conducting
element; a current sensor; and a current control element coupled in
series with said current conducting element and said current sensor
and conductive in response to a control signal, wherein said
current sensor comprises: a current sensing element coupled in
series between said current conducting element and said current
control element; a subtractor for providing an error signal
representative of a difference between a current conducted by said
current sensing element and a target current when said current
control element is conductive; and an integrator for forming an
integrated error signal by integrating said error signal.
18. The current regulated circuit of claim 17 further comprising: a
control circuit having an input for receiving said integrated error
signal, and an output for providing said control signal.
19. The current regulated circuit of claim 17, wherein: said
control element comprises a current conduction element of a sense
transistor; and said current sensing element comprises a drain
sense element of said sense transistor.
20. The current regulated circuit of claim 19, wherein said
subtractor comprises: a target current source having a first
terminal coupled to a voltage reference terminal, and a second
terminal coupled to said drain sense element of said sense
transistor; a first switch having a first terminal coupled to said
current conduction element of said sense transistor, a second
terminal for providing a first component of said error signal, and
a control terminal for receiving said control signal; and a second
switch having a first terminal coupled to said drain sense element
of said sense transistor, a second terminal for providing a second
component of said error signal, and a control terminal for
receiving said control signal.
21. The current regulated circuit of claim 19, wherein said
subtractor comprises: an amplifier having a first input coupled to
said current conduction element of said sense transistor, a second
input coupled to said drain sense element of said sense transistor,
and an output; a target current source having a first terminal
coupled to a voltage reference terminal, and a second terminal; and
a transistor having a first current electrode coupled to said
second terminal of said target current source, a control electrode
coupled to said output of said amplifier, and a second current
electrode coupled to said drain sense element of said sense
transistor; and a switch having a first terminal coupled to said
second terminal of said target current source, a second terminal
for providing said error signal, and a control terminal for
receiving said control signal.
22. A method comprising: coupling a current sensing element in a
current conduction path of a current regulated circuit; developing
a sensed signal from a first terminal of said current sensing
element; developing a target signal in response to a characteristic
of a circuit element matched to said current sensing element from a
second terminal of said current sensing element; forming an error
signal in response to a difference between said sensed signal and
said target signal; and regulating a current flow through said
current conduction path in response to said error signal.
23. The method of claim 22, wherein said coupling said current
sensing element in said current conduction path of said current
regulated circuit comprises coupling a sense resistor in said
current conduction path of said current regulated circuit.
24. The method of claim 22, wherein said coupling said current
sensing element in said current conduction path of said current
regulated circuit comprises coupling a sense transistor in said
current conduction path of said current regulated circuit.
25. The method of claim 24, wherein: coupling said sense transistor
in said current conduction path of said current regulated circuit
comprises coupling a current conduction element of said sense
transistor in said current conduction path of said current
regulated circuit; and developing said target signal in response to
said characteristic of said circuit element comprises developing
said target signal in response to said characteristic of a drain
sense element of said sense transistor.
Description
FIELD OF THE DISCLOSURE
[0001] The present application relates generally to electrical
sensors, and more particularly, to current sense elements and
current regulated circuits using current sense elements.
BACKGROUND
[0002] Various electromechanical systems use solenoids to switch or
actuate high current circuits. For example in automobiles, a
transmission system uses a shifting handle to mechanically activate
a solenoid to engage a set of gears. In another example, an
ignition key or button uses a solenoid to engage a starter motor.
In yet another example, an anti-lock braking system (ABS)
electronically engages automobile brakes in a controlled manner to
prevent wheel lockup and skidding. The electronic controllers in
these systems need to accurately regulate the amount of current
through the solenoids. For example a transmission control unit
(TCU) for a transmission system may regulate a solenoid current to
1-2 amperes (A) with an accuracy of about 1.5% or less.
[0003] Electronic controllers use a current sense element along a
feedback loop to regulate to perform accurate current regulation.
It is difficult to design current sense elements that are both
inexpensive and also achieve the required accuracy. For example a
typical current sense element circuit detects current by measuring
a voltage across a low-valued resistor connected in series with the
solenoid. If the value of the resistor is substantially constant,
then the measured voltage is proportional to the current with the
required accuracy. However the values of the sensing resistors vary
with temperature and over their operating lifetimes. Moreover these
variances become worse when the resistor is combined with other
components in an inexpensive semiconductor integrated circuit. In
addition, the amplifier that is used to measure the voltage is also
susceptible to various sources of inaccuracy such as gain accuracy
when operating with a large common mode voltage and temperature
drift. To overcome these problems, known current sense elements
have used various trimming and calibration techniques, but these
techniques increase system complexity and cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 illustrates in partial block diagram and partial
schematic form a current regulated circuit according to the prior
art;
[0005] FIG. 2 illustrates in partial block diagram and partial
schematic form a current regulated circuit according to an
embodiment;
[0006] FIG. 3 illustrates in partial block diagram and partial
schematic form a current regulated circuit according to an
embodiment of the current regulated circuit of FIG. 2;
[0007] FIG. 4 illustrates in partial block diagram and partial
schematic form a current regulated circuit according to another
embodiment of the current regulated circuit of FIG. 2;
[0008] FIG. 5 illustrates in partial block diagram and partial
schematic form an integrator suitable for use in a current
regulated circuit;
[0009] FIG. 6 illustrates in partial block diagram and partial
schematic form a current regulated circuit according to yet another
embodiment of the current regulated circuit of FIG. 2;
[0010] FIG. 7 illustrates in schematic form a portion of a current
regulated circuit showing a first form of a target signal
generator;
[0011] FIG. 8 illustrates in schematic form a portion of a current
regulated circuit showing a second form of a target signal
generator;
[0012] FIG. 9 illustrates in schematic form a segmented resistor
suitable for use in the target signal generators of FIGS. 3, 7, and
8;
[0013] FIG. 10 illustrates in block diagram form a current source
suitable for use in the target signal generators of FIGS. 3, 4, and
6-8;
[0014] FIG. 11 illustrates in block diagram form a voltage source
suitable for use in the target signal generators of FIGS. 7 and
8;
[0015] FIG. 12 illustrates in partial block diagram and partial
schematic form a current regulated circuit according to a further
embodiment of the current regulated circuit of FIG. 2;
[0016] FIG. 13 illustrates in partial block diagram and partial
schematic form a current regulated circuit according to a still
further embodiment of the current regulated circuit of FIG. 2;
[0017] FIG. 14 illustrates in block diagram form a first digital
converter circuit that may be used in the current regulated circuit
of FIG. 2;
[0018] FIG. 15 illustrates in block diagram form a second digital
converter circuit that may be used in the current regulated circuit
of FIG. 2;
[0019] FIG. 16 illustrates in partial block diagram and partial
schematic form a third digital converter circuit that may be used
in the current regulated circuit of FIG. 2;
[0020] FIG. 17 illustrates in partial block diagram and partial
schematic form a fourth digital converter circuit that may be used
in the current regulated circuit of FIG. 2; and
[0021] FIG. 18 illustrates in schematic form a sense transistor
that can be used in any of the current regulated circuits of FIGS.
4, 6, 12, and 13.
[0022] In the following description, the use of the same reference
numerals in different drawings indicates similar or identical
items. Unless otherwise noted, the word "coupled" and its
associated verb forms include both direct connection and indirect
electrical connection by means known in the art, and unless
otherwise noted any description of direct connection implies
alternate embodiments using suitable forms of indirect electrical
connection as well.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0023] FIG. 1 illustrates in partial block diagram and partial
schematic form a current regulated circuit 100 according to the
prior art. Current regulated circuit 100 includes a solenoid 110, a
current sense element 120, a transistor 130, a digital signal
processor (DSP) 140, and a diode 150. Solenoid 110 has a first
terminal for receiving a power supply voltage labeled "V.sub.BAT",
and a second terminal. V.sub.BAT is a power supply voltage from a
battery having a nominal voltage of, for example, 12 volts with
respect to ground. Current sense element 120 has a first terminal
connected to the second terminal of solenoid 110, a second
terminal, and an output terminal. Transistor 130 is an N-channel
metal-oxide-semiconductor (MOS) transistor having a drain connected
to the second terminal of current sense element 120, a gate, and a
source connected to ground. DSP 140 has an input connected to the
output terminal of current sense element 120, and an output
connected to the gate of transistor 130. Diode 150 has an anode
connected to the second terminal of current sense element 120, and
a cathode connected to the V.sub.BAT power supply voltage
terminal.
[0024] Current sense element 120 includes a resistor 122, an
amplifier 124, and an analog-to-digital converter (ADC) 126.
Resistor 122 has a first terminal forming the first terminal of
current sense element 120, and a second terminal forming the second
terminal of current sense element 120. Amplifier 124 has a
non-inverting input connected to the first terminal of resistor
122, an inverting terminal connected to the second terminal of
resistor 122, and an output. ADC 126 has an input connected to the
output of amplifier 124, and an output connected to the input of
DSP 140.
[0025] Current regulated circuit 100 regulates the current flow
through solenoid 110. When activated, current regulated circuit 100
causes current to flow through solenoid 110 at a magnitude that is
regulated to a desired amount. Current sense element 120 provides a
digital representation of the magnitude of the current through
solenoid 110, and DSP 140 digitally regulates it to the desired
amount by controlling the on time of transistor 130. Diode 150
provides a clamping path to prevent the voltage at the drain of
transistor 130 from rising above V.sub.BAT by more than its cutoff
voltage, and thus protects transistor 130 from damage due to
excessive voltage at its drain when transistor 130 is
non-conductive.
[0026] Current sense element 120 detects the voltage drop across
resistor 122 as a measure of the current flowing through solenoid
110. Amplifier 124 senses and amplifies the voltage difference and
provides the voltage difference as a single-ended voltage to ADC
126. ADC 126 converts the voltage to a corresponding digital value,
which DSP 140 uses to modulate the conduction of transistor 130 to
regulate the current flow to a desired value.
[0027] Current sense element 120 has several disadvantages. The
current through solenoid 110 is expected to be regulated to a high
degree of accuracy, but resistor 122 suffers from drift over
temperature and over its lifetime. In addition, the large power
dissipation through resistor 122 and transistor 130 cause a large
temperature gradient within an integrated circuit die. Since
resistor 122 is a floating sensing element, it is difficult to
sense the voltage across its terminals. Resistor 122 is also costly
due to its required precision.
[0028] FIG. 2 illustrates in partial block diagram and partial
schematic form a current regulated circuit 200 according to an
embodiment. Current regulated circuit 200 includes a current
conducting element in the form of a solenoid 210, a current sense
element 220, a transistor 230, a transistor 232, and a control
circuit 240. Solenoid 210 has a first terminal for receiving
V.sub.BAT, and a second terminal. Current sense element 220 has a
first terminal connected to the second terminal of solenoid 210, a
second terminal, and an output terminal for providing a signal
labeled "ERROR SIGNAL". Transistor 230 is an N-channel MOS
transistor having a drain connected to the second terminal of
current sense element 220, a gate, and a source connected to
ground. Transistor 232 is a P-channel MOS transistor having a
source connected to the VBAT terminal, a gate, and a drain
connected to the second terminal of solenoid 210. Control circuit
240 has an input connected to the output terminal of current sense
element 220 for receiving the ERROR SIGNAL, and an output connected
to the gate of transistor 230. Diode 250 has an anode connected to
the second terminal of current sense element 220, and a cathode
connected to the V.sub.BAT power supply voltage terminal.
[0029] Current sense element 220 includes a current sense element
222, a target signal generator 224, and an error signal generator
226. Current sense element 222 has a first terminal forming the
first terminal of current sense element 220, a second terminal
forming the second terminal of current sense element 220, a first
output for providing a signal labeled "MEASURED SIGNAL", and a
second output. Target signal generator 224 has an input connected
to the second output of current sense element 222, and an output
for providing a signal labeled "TARGET SIGNAL". Error signal
generator 226 has a first input connected to the first output of
current sense element 222 for receiving the MEASURED SIGNAL, a
second input connected to the output of target signal generator 224
for receiving the TARGET signal, and an output connected to the
input of control circuit 240 for providing the ERROR SIGNAL.
[0030] In operation, current sense element 222 is connected in a
current path whose current is to be sensed, such as a solenoid
current control circuit as in current regulated circuit 200. It
provides two outputs representative of the current flowing through
it. Target signal generator 224 generates the TARGET SIGNAL as a
signal representative of a condition of current sense element 222
when current sense element 222 conducts a target current. Error
signal generator 226 has an output for providing the ERROR SIGNAL
as the difference between the current actually flowing through
current sense element 222, i.e. the MEASURED SIGNAL, and the TARGET
SIGNAL.
[0031] As will be described more fully below, current sense element
222 can be, for example, a resistor or the drain sense element of a
sense transistor. Target signal generator 224 generates the TARGET
SIGNAL to represent a condition of current sensing element 222 when
current sensing element 222 conducts a target current. In one
example, target signal generator 224 generates the TARGET SIGNAL as
a voltage drop across current sense element 222 when current sense
element 222 conducts the target current, and thus the input is
connected to the second output of current sense element 222 to
adjust its output based on, for example, the voltage on the second
terminal of current sense element 222. In another example, target
signal generator 224 generates the TARGET SIGNAL as the current
passing through current sense element 222 when current sense
element 222 generates the target current.
[0032] Thus target signal generator 224 outputs the TARGET SIGNAL
as a target or reference to which the actual value can be compared.
To generate a useful value, target signal generator 224 does not
need to provide the TARGET SIGNAL with high absolute accuracy as
long as the component it uses matches current sense element
222.
[0033] Error signal generator 226 provides the ERROR SIGNAL in
response to the difference between the MEASURED SIGNAL and the
TARGET SIGNAL. Control circuit 240 modulates the on time of
transistor 230 to reduce the magnitude of the ERROR SIGNAL. Thus
current regulated circuit 200 controls transistor 230 in order to
null the ERROR SIGNAL, or stated another way, to make the MEASURED
SIGNAL equal to the TARGET SIGNAL.
[0034] Current sense element 220 provides various advantages over
known current sense element designs and over the current regulated
circuits that use them. First, by subtracting the TARGET SIGNAL
from the MEASURED SIGNAL and regulating the loop based on the ERROR
SIGNAL, current regulated circuit 200 avoids the need for high
precision, costly components such as high precision resistors. The
only need is for the component (such as a resistor) in target
signal generator 224 to be matched to the component used in current
sense element 222. Thus cheaper and possibly integrated components
can be used. Second, current regulated circuit 200 does not
experience significant temperature and lifetime sensitivity.
Because they are matched, current sense element 222 and target
signal generator 224 may drift over temperature and over their
lifetimes, but their drifts will tend to match and therefore cancel
each other out. Third, by generating the ERROR SIGNAL as the
difference between the MEASURED SIGNAL and the TARGET SIGNAL,
current sense element 220 avoids problems caused by the floating
reference. Note that target signal generator 224 uses an output of
current sense element 222 so that it is referenced to the same
floating node.
[0035] There are a variety of circuits that can be used to
implement the components of current regulated circuit 200. These
various circuits will be explained first with reference to specific
examples of current regulated circuits, as well as specific
components on an element by element basis.
[0036] FIG. 3 illustrates in partial block diagram and partial
schematic form a current regulated circuit 300 according to an
embodiment of current regulated circuit 200 of FIG. 2. Current
regulated circuit 300 includes generally a current conducting
element in the form of a solenoid 310, a current sense element 320,
transistors 330 and 332, a control circuit 340, and buffers 342 and
344. Solenoid 310 has a first terminal for receiving V.sub.BAT, and
a second terminal. Current sense element 320 has a first terminal
connected to the second terminal of solenoid 310, a second
terminal, and an output terminal for providing an error signal in
the form of a difference current labeled ".DELTA.I". Transistor 330
is an N-channel MOS transistor having a drain connected to the
second terminal of current sense element 320, a gate, and a source
connected to ground. Transistor 332 is an P-channel MOS transistor
having a source connected to the V.sub.BAT terminal, a gate, and a
drain connected to the second terminal of current sense element
320. Control circuit 340 has an input connected to the output
terminal of current sense element 320 for receiving error signal
.DELTA.I, a first output connected to the gate of transistor 330,
and a second output connected to the gate of transistor 332. Buffer
342 has an input connected to the first output of control circuit
340, and a second output connected to the gate of transistor 330.
Buffer 344 has an input connected to the second output of control
circuit 340, and a second output connected to the gate of
transistor 332.
[0037] Current sense element 320 includes a resistor 322, a target
signal generator 324, and an error signal generator 326. Resistor
322 has a first terminal forming the first terminal of current
sense element 320, and a second terminal forming the second
terminal of current sense element 320, in which the first terminal
also forms a the MEASURED SIGNAL.
[0038] Target signal generator 324 has a first terminal connected
to the V.sub.BAT terminal, a second terminal connected to the
second terminal of resistor 322, and an output for providing the
TARGET SIGNAL. Target signal generator 324 includes a current
source 323 and a resistor 325. Current source 323 has a first
terminal connected to the V.sub.BAT terminal, and a second terminal
for providing the TARGET SIGNAL, and conducts a current labeled
"I.sub.TARG". Resistor 325 has a first terminal connected to the
second terminal of current source 323, and a second terminal
connected to the second terminal of resistor 322, and has a
resistance labeled "R.sub.MATCHED".
[0039] Error signal generator 226 has a first input connected to
the first output of current sense element 222 for receiving the
MEASURED SIGNAL, a second input connected to the output of target
signal generator for receiving the TARGET SIGNAL, and an output
connected to the input of control circuit 340 for providing the
ERROR SIGNAL. Error signal generator 326 includes an amplifier 327
and an ADC 328. Amplifier 327 includes a non-inverting input for
receiving the MEASURED SIGNAL, an inverting input for receiving the
TARGET SIGNAL, and an output. ADC 328 has an input connected to the
output of amplifier 326, and an output for providing error signal
.DELTA.I.
[0040] Current regulated circuit 300 implements target signal
generator 224 of FIG. 2 by forming the TARGET SIGNAL as a voltage
representative of the voltage formed at the first terminal of
resistor 322 when solenoid 310 conducts the desired amount of
current. Current source 323 sources current I.sub.TARG as a current
proportional to the desired amount of current. Resistor 325
provides resistance R.sub.MATCHED that is inversely proportional to
the resistance of resistor 322, in the same proportionality as
I.sub.TARG is to the target current through solenoid 310. For
example if the desired current through solenoid 310 is equal to 1 A
and the nominal resistance of resistor 322 is equal to 1 ohm
(.OMEGA.), then if I.sub.TARG is equal to 1 milliampere (mA), then
R.sub.MATCHED would be set to 1 kilohm (k.OMEGA.). When the
elements of current sense element 320 are combined in a single
integrated circuit, resistor 325 may also be matched to resistor
322 by layout on the integrated circuit. The layout matching can
include, for example, the orientation on the integrated circuit
such that variations in processing in a certain direction will
affect both resistors proportionally.
[0041] Since .DELTA.I is a digital value, control circuit 340 can
be implemented as a DSP. Control circuit 340 uses buffer 342 to
drive the gate of transistor 330 and buffer 344 to drive the gate
of transistor 332. Current regulated circuit 300 uses transistor
332 as a synchronous clamp such that it is conductive generally
during times when transistor 330 is nonconductive, except that
there is a sufficient amount of non-overlap time to avoid shoot
through currents.
[0042] Thus current sense element 320 uses two resistors to develop
a digital error signal .DELTA.I. The resistors need not have highly
accurate values as long as they are properly matched, e.g. in both
size and layout.
[0043] FIG. 4 illustrates in partial block diagram and partial
schematic form a current regulated circuit 400 according to another
embodiment of current regulated circuit 200 of FIG. 2. Current
regulated circuit 400 includes generally a current conducting
element in the form of a solenoid 410, a target and error signal
generator 420, a sense transistor 430, a transistor 436, a control
circuit 440, and buffers 442 and 444. Solenoid 410 has a first
terminal for receiving V.sub.BAT, and a second terminal. Target and
error signal generator 420 includes an amplifier 422, a current
source 424, and a transistor 426. Amplifier 422 has a non-inverting
input connected to the second terminal of solenoid 410, an
inverting input, and an output. Current source 424 has a first
terminal connected to the V.sub.BAT terminal, and a second
terminal, and conducts current I.sub.TARG. Transistor 426 has a
drain connected to the second terminal of current source 424, a
gate connected to the output of amplifier 422, and a source
connected to the inverting input of amplifier 422.
[0044] Sense transistor 430 has a drain connected to the second
terminal of solenoid 410 and to the non-inverting input of
amplifier 422, a sense drain connected to the inverting input of
amplifier 422 and to the source of transistor 426, a gate, and a
source connected to ground. Sense transistor 430 is a composite
N-channel MOS power transistor having a drain terminal, a sense
drain terminal, a gate, and a source. Sense transistor 430 is
formed using a current conduction element 432 and a drain sense
element 434. Current conduction element 432 has a drain forming the
drain terminal (D) of sense transistor 430, a gate connected to the
gate terminal (G) of sense transistor 430, and a source connected
to the source terminal (S) of sense transistor 430. Drain sense
element 434 has a drain forming the sense drain terminal (SD) of
sense transistor 430, a gate connected to the gate terminal of
sense transistor 430, and a source connected to the source terminal
of sense transistor 430. Transistor 436 is a P-channel MOS
transistor having a source connected to the V.sub.BAT terminal, a
gate, and a drain connected to the second terminal of solenoid
410.
[0045] Control circuit 440 has an input connected to the second
terminal of current source 424, a first output, and a second
output. Buffer 442 has an input connected to the first output of
control circuit 440, and an output connected to the gate of sense
transistor 430. Buffer 444 has an input connected to the second
output of control circuit 440, and an output connected to the gate
of transistor 432.
[0046] Sense transistor 430 implements portions of current sense
element 220 and transistor 230 of FIG. 2. Current conduction
element 434 operates as both current sense element 222 and
transistor 230. Drain sense element 436 operates as part of target
signal generator 224. Amplifier 422 and transistor 426 operate as
the other portion of current sense element 222. Current source 424
operates as target signal generator 224 providing the TARGET
SIGNAL. Current source 424, amplifier 422, and transistor 426
operate as error signal generator 226. Amplifier 422 controls the
conductivity of transistor 426 to output the MEASURED SIGNAL. The
difference between the MEASURED SIGNAL and the TARGET SIGNAL
provides an analog error signal .DELTA.I. Control circuit 440 can
be an analog control circuit or, with the addition of an ADC, a
digital control circuit such as a DSP.
[0047] Current regulated circuit 400 has generally the same
benefits as current regulated circuit 300 of FIG. 3, but by the use
of sense transistor 430, it has a smaller area and lower power
dissipation than current regulated circuit 300. Also while the
input offset of amplifier 422 is kept low, there is no need for it
to have an accurate gain.
[0048] FIG. 5 illustrates in partial block diagram and partial
schematic form an integrator 500 suitable for use in a current
regulated circuit. Integrator 500 includes an amplifier 510 and a
capacitor 520. Amplifier 510 has a non-inverting input for
receiving error signal .DELTA.I, an inverting input for receiving a
reference voltage labeled "V.sub.REF", and an output for providing
a signal labeled "INTEGRATED ERROR CURRENT". Capacitor 520 has a
first terminal connected to the output of amplifier 510, and a
second terminal connected to the non-inverting input of amplifier
510. Integrator 500 is useful in smoothing changes in error signal
.DELTA.I so that the control loop is stable. Integrator 500 can be
used to integrate the error signal over a switching period or over
the conduction time, for example the conduction time of sense
transistor 430, by inserting the integrator 500 between the error
signal generator providing the error signal .DELTA.I and the
control circuit 440. It is useful in several current regulated
circuits including the one which will now be described.
[0049] FIG. 6 illustrates in partial block diagram and partial
schematic form a current regulated circuit 600 according to yet
another embodiment of current regulated circuit 200 of FIG. 2.
Current regulated circuit 600 includes generally a current
conducting element in the form of a solenoid 610, a target and
error signal generator 620, sense transistor 630, transistor 632, a
control circuit 640, and buffers 642 and 644. Solenoid 610 has a
first terminal for receiving V.sub.BAT, and a second terminal.
[0050] Target and error signal generator 620 includes an amplifier
621, a transistor 622, a current source 623, an amplifier 624, a
transistor 625, switches 626 and 627, and an integrator 628.
Amplifier 621 has a non-inverting input connected to the V.sub.BAT
terminal, an inverting input, and an output. Transistor 622 is a
P-channel MOS transistor having a source connected to the inverting
input of amplifier 621, a gate connected to the output of amplifier
621, and a drain. Current source 623 has a first terminal connected
to the drain of transistor 622, and a second terminal, and conducts
current I.sub.TARG. Amplifier 624 has a non-inverting input
connected to the second terminal of solenoid 610, an inverting
input, and an output. Transistor 625 is a N-channel MOS transistor
having a drain connected to the second terminal of current source
623, a gate connected to the output of amplifier 624, and a source
connected to the inverting input of amplifier 624. Switch 626 has a
first terminal connected to the drain of transistor 622, a second
terminal, and a control terminal. Switch 627 has a first terminal
connected to the drain of transistor 625, a second terminal
connected to the second terminal of switch 626, and a control
terminal. Integrator 628 has an input connected to the second
terminals of switches 626 and 627, and an output for providing the
INTEGRATED ERROR CURRENT.
[0051] Sense transistor 630 is a composite N-channel MOS power
transistor having a drain connected to the second terminal of
solenoid 610 and to the non-inverting input of amplifier 624, a
sense drain connected to the inverting input of amplifier 624 and
to the source of transistor 625, a gate, and a source connected to
ground. Sense transistor 632 is a composite N-channel MOS power
transistor having a drain terminal connected to the V.sub.BAT node,
a sense drain terminal connected to the inverting input of
amplifier 621, a gate, and a source connected to the second
terminal of solenoid 610.
[0052] Control circuit 640 has an input connected to the output of
integrator 628, a first output, and a second output. Buffer 642 has
an input connected to the first output of control circuit 640, and
an output connected to the gate of sense transistor 630 and to the
control terminal of switch 627. Buffer 644 has an input connected
to the second output of control circuit 640, and an output
connected to the gate of transistor 632 and to the control terminal
of switch 626.
[0053] Current regulated circuit 600 uses a differential
architecture to develop the net current through solenoid 610 during
on and off times. When current is being conducted through solenoid
610, sense transistor 630 is conductive, sense transistor 632 is
non-conductive, buffer 644 opens switch 626, and buffer 642 closes
switch 627. Amplifier 621 drives a voltage onto the gate of
transistor 622 to make it conductive. When current is being not
conducted through solenoid 610, sense transistor 632 is conductive,
sense transistor 630 is non-conductive, buffer 644 closes switch
626, and buffer 642 opens switch 627. Amplifier 624 drives a
voltage onto the gate of transistor 625 to make it conductive to
zero out.
[0054] The components of current regulated circuit 200 of FIG. can
be implemented in a variety of ways, such as the ways shown in the
exemplary embodiments of FIGS. 3, 4, and 6. These and several
additional ways will now be described.
[0055] FIG. 7 illustrates in schematic form a portion 700 of a
current regulated circuit showing a first form of a target signal
generator. Portion 700 includes a resistor 722 operating as a
current sense element, a target voltage source 710, and a
difference amplifier 730. As in the other embodiments, resistor 722
has first and second terminals connected in a current conduction
path of an inductive element in the form of a solenoid whose
current is to be regulated to a desired value. Target voltage
source 710 has a negative terminal connected to the second terminal
of resistor 722, and a positive terminal for providing the TARGET
SIGNAL, and provides a voltage labeled "V.sub.TARG". Difference
amplifier 730 has a non-inverting input connected to the first
terminal of resistor 722, an inverting input connected to the
second terminal of resistor 722, and an output for providing the
MEASURED SIGNAL. FIG. 7 shows that an error signal labeled
"V.sub.ERROR" is represented as the difference between the MEASURED
SIGNAL and the TARGET SIGNAL. FIG. 7 also shows target voltage
source 710 implemented with a current source 712 and a resistor
714. Current source 712 has a first terminal connected to the
V.sub.BAT terminal, and a second terminal for providing the TARGET
SIGNAL, and conducts current I.sub.TARG. Resistor 714 has a first
terminal connected to the second terminal of current source 712,
and a second terminal connected to the second terminal of resistor
722, and has resistance R.sub.MATCHED. The TARGET SIGNAL is equal
to V.sub.TARG plus the voltage at the second terminal of resistor
722.
[0056] FIG. 8 illustrates in schematic form a portion 800 of a
current regulated circuit showing a second form of a target signal
generator. Portion 800 includes a resistor 822 operating as a
current sense element and a target voltage source 810. Resistor 822
has first and second terminals connected in a current conduction
path of an inductive element in the form of a solenoid whose
current is to be regulated to a desired value. Target voltage
source 810 has a positive terminal connected to the first terminal
of resistor 822, and a negative terminal for providing the TARGET
SIGNAL, and provides a voltage V.sub.TARG. FIG. 8 shows that an
error signal labeled "V.sub.ERROR" is represented as the difference
between the TARGET SIGNAL added to V.sub.TARG, and a reference
voltage at the second terminal of resistor 822. FIG. 8 also shows
target voltage source 810 implemented with a resistor 812 and a
current sink 814. Resistor 812 has a first terminal connected to
the first terminal of resistor 822, and a second terminal for
providing the MEASURED SIGNAL--V.sub.TARG. Current source 814 has a
first terminal connected to the second terminal of resistor 812,
and a second terminal connected to ground, and conducts current
I.sub.TARG. In portion 800, V.sub.ERROR is again equal to the
MEASURED SIGNAL minus the TARGET SIGNAL, but V.sub.ERROR is
developed differently than the way it is developed in FIG. 7.
[0057] FIG. 9 illustrates in schematic form a segmented resistor
900 suitable for use in the target signal generators of FIGS. 3, 7,
and 8. Segmented resistor 900 includes a resistor ladder 910 and a
multiplexer 920. Resistor ladder 910 is formed using a set of
resistive segments connected in series. Shown in FIG. 9 is a
representative set of resistive segments 912, 914, and 916, in
which resistive segment 912 has a first terminal connected to the
first terminal of segmented resistor 900, and a second terminal,
resistive segment 914 has a first terminal connected to the second
terminal of resistive segment 912, and a second terminal, and so on
until resistive segment 916 that has a first terminal connected to
the second terminal of the immediately preceding resistive segment
in the series, and a second terminal connected to the second
terminal of segmented resistor 900. Multiplexer 920 has inputs
connected to terminals of respective ones of the set of resistors
in resistor ladder 910, an output for providing the V.sub.TARG
signal, and a control terminal for receiving a control signal
labeled "SEL".
[0058] Segmented resistor 900 allows the resistor to be
programmably matched to the sense resistor for a variety of
different currents. The value of the resistance is set based on the
SEL signal and the selected connection point on the ladder
determines the value of the resistance. For example, if segmented
resistor 900 is used to implement resistor 714 of FIG. 7 and if the
matched value includes all but one resistor segment, then the SEL
signal selects the first input thereof, the output of multiplexer
920 forms the first terminal of resistor 714, and the second
terminal of resistive segment 916 forms the second terminal of
resistor 714 and is connected to the second terminal of resistor
722 Conversely if segmented resistor 900 is used to implement
resistor 812 of FIG. 8 and if the matched value includes two
resistor segments, then the SEL signal selects the second input
thereof, the first terminal of resistive segment 912 forms the
first terminal of resistor 812, and the output of multiplexer 920
forms the second terminal of resistor 812.
[0059] FIG. 10 illustrates in block diagram form a current source
1000 suitable for use in the target signal generators of FIGS. 3,
4, and 6-8. Current source 1000 is implemented using a current
digital-to-analog converter (DAC) that has an input for receiving a
multi-bit input code, a reference input for receiving a reference
current, and an output for providing current I.sub.TARG. By being
programmable, current source 1000 can be used in a current sense
element with the configurations such as those of FIGS. 2, 3, and
6-8 but adapted for different application environments by providing
a range of target currents.
[0060] FIG. 11 illustrates in block diagram form a voltage source
1100 suitable for use in the target signal generators of FIGS. 7
and 8. Voltage source 1100 is implemented using a voltage DAC that
has an input for receiving a multi-bit input code, a reference
input for receiving a reference voltage, a signal input coupled to
the sense resistor, and an output for providing voltage V.sub.TARG.
By being programmable, voltage source 1100 can be used in a current
sense element with the configurations of FIGS. 7 and 8 but adapted
for different application environments providing for a range of
target voltages.
[0061] FIG. 12 illustrates in partial block diagram and partial
schematic form a current regulated circuit 1200 according to a
further embodiment of current regulated circuit 200 of FIG. 2.
Current regulated circuit 1200 includes generally a current
conducting element in the form of a solenoid 1210, a target and
error signal generator 1220, a sense transistor 1230, a transistor
1236, and a control circuit 1240. Solenoid 1210 has a first
terminal for receiving V.sub.BAT, and a second terminal. Current
sense portion 1220 includes a current source 1221, switches 1222
and 1223, and a subtractor 1224. Current source 1221 has a first
terminal connected to the V.sub.BAT terminal, and a second
terminal, and conducts current I.sub.TARG. Switch 1222 has a first
terminal connected to the second terminal of solenoid 1210, a
second terminal, and a control terminal. Switch 1223 has a first
terminal connected to the sense drain terminal of transistor 1220,
a second terminal, and a control terminal. Subtractor 1224 has a
first input connected to the second terminal of switch 1222, a
second terminal connected to the second terminal of switch 1223,
and an output terminal for providing the INTEGRATED ERROR SIGNAL.
Subtractor 1224 includes an optional resistor 1225, an amplifier
1226, and a capacitor 1227. Resistor 1225 has a first terminal
connected to the second terminal of switch 1222, and a second
terminal. Amplifier 1226 has a non-inverting input connected to the
second terminal of resistor 1225, an inverting input connected to
the second terminal of switch 1223, and an output for providing the
INTEGRATED ERROR SIGNAL. Capacitor 1227 has a first terminal
connected to the output terminal of amplifier 1226, and a second
terminal connected to the non-inverting input of amplifier
1226.
[0062] Sense transistor 1230 has a drain connected to the second
terminal of solenoid 1210 and to the first terminal of switch 1223,
a sense drain connected to the second terminal of current source
1221 and to the first terminal of switch 1223, a gate, and a source
connected to ground. Sense transistor 1230 is a composite N-channel
MOS power transistor having a drain terminal, a sense drain
terminal, a gate, and a source. Sense transistor 1230 is formed
using a current conduction element 1232 and a drain sense element
1234. Current conduction element 1232 has a drain forming the drain
terminal of sense transistor 1230, a gate connected to the gate
terminal of sense transistor 1230, and a source connected to the
source terminal of sense transistor 1230. Drain sense element 1234
has a drain forming the sense drain terminal of sense transistor
1230, a gate connected to the gate terminal of sense transistor
1230, and a source connected to the source terminal of sense
transistor 1230. Transistor 1236 is a P-channel MOS transistor
having a source connected to the V.sub.BAT terminal, a gate, and a
drain connected to the second terminal of solenoid 410.
[0063] Control circuit 1240 has an input connected to the output of
amplifier 1226, a first output connected to the gate of transistor
1230 and to the control terminals of switches 1222 and 1223, and a
second output connected to the gate of transistor 1236. As shown in
FIG. 12, control circuit 1240 includes a buffer 1242 having an
output forming the first output of control circuit 1240.
[0064] Current regulated circuit 1200 uses sense transistor 1230 in
a manner similar to current regulated circuit 400 of FIG. 4, but
uses a different target and error signal generator 1220. Current
sensing circuit 1220 includes subtractor 1224 as an integrating
subtractor that, through switches 1222 and 1223, is synchronized to
the switching activity. Thus when sense transistor 1230 is
conductive, switches 1222 and 1223 are closed, and subtractor 1224
integrates the difference between the MEASURED SIGNAL and the
TARGET SIGNAL. When sense transistor 1230 is non-conductive,
switches 1222 and 1223 are open, and subtractor 1224 retains the
integrated difference between the MEASURED SIGNAL and the TARGET
SIGNAL.
[0065] FIG. 13 illustrates in partial block diagram and partial
schematic form a current regulated circuit 1300 according to a
still further embodiment of the current regulated circuit of FIG.
2. Current regulated circuit 1300 includes generally a current
conducting element in the form of a solenoid 1310, a target and
error signal generator 1320, a sense transistor 1330, a transistor
1332, and a control circuit 1340. Solenoid 1310 has a first
terminal for receiving V.sub.BAT, and a second terminal. Target and
error signal generator 1320 includes an amplifier 1321, a current
source 1322, a transistor 1323, a switch 1324, and an integrator
1325. Amplifier 1321 has a non-inverting input connected to the
second input of solenoid 1310, an inverting input, and an output.
Current source 1322 has a first terminal connected to the V.sub.BAT
terminal, and a second terminal, and conducts current I.sub.TARG.
Transistor 1323 has a drain connected to the second terminal of
current source 1322, a gate connected to the output of amplifier
1321, and a source connected to the inverting input of amplifier
1321. Switch 1324 has a first terminal connected to the second
terminal of current source 1322, a second terminal, and a control
terminal. Integrator 1325 has an input terminal connected to the
second terminal of switch 1324, and an output terminal for
providing the INTEGRATED ERROR SIGNAL.
[0066] Sense transistor 1330 has a drain connected to the second
terminal of solenoid 1310, a sense drain connected to the inverting
input of amplifier 1321 and to the source of transistor 1323, a
gate, and a source connected to ground. Sense transistor 1330 is a
composite N-channel MOS power transistor constructed as described
with respect to FIG. 4 above. Transistor 1332 is a P-channel MOS
transistor having a source connected to the V.sub.BAT terminal, a
gate, and a drain connected to the second terminal of solenoid
1310.
[0067] Control circuit 1340 has an input connected to the output of
integrator 1325, a first output connected to the gate of transistor
1330 and to the control terminal of switches 1324, and a second
output connected to the gate of transistor 1332. As shown in FIG.
12, control circuit 1340 includes a buffer 1342 having an output
forming the first output of control circuit 1340.
[0068] Current regulated circuit 1300 provides an error signal as a
differential current .DELTA.I using a sense transistor 1330,
integrates the differential current during the conduction time of
solenoid 1310 to provide the INTEGRATED ERROR SIGNAL, and controls
the on time of sense transistor 1330 to regulate the current of
solenoid 1310 to a desired amount. Thus it is a modification of
current regulated circuit 400 of FIG. 4 by using switch 1324 and
integrator 1325 to limit the control during conduction times of
transistor 1330.
[0069] Various modifications to the circuits described above can be
made in order to provide a more robust signal path and also to
convert from the floating ground domain of the current sensing
resistor to the controller domain. These modifications will now be
described.
[0070] FIG. 14 illustrates in block diagram form a first digital
converter circuit 1400 that may be used in current regulated
circuit 200 of FIG. 2. Digital converter circuit 1400 is a
comparator having a non-inverting input, an inverting input, and an
output for providing a single-bit error signal labeled "DIGITAL
ERROR SIGNAL", in which a differential integrated error voltage
labeled "V.sub.EI" is sensed between the non-inverting and
inverting inputs. In this case, a control circuit such as a DSP can
either filter and process the single bit signal, or decimate the
sequence of bits over a certain period of time to form a multi-bit
digital code and filter and process the multi-bit digital code.
[0071] FIG. 15 illustrates in block diagram form a second digital
converter circuit 1500 that may be used in current regulated
circuit 200 of FIG. 2. Digital converter circuit 1500 is an ADC
having an input for receiving an integrated error voltage V.sub.EI
as a single-ended error signal, and an output for providing a
multiple-bit DIGITAL ERROR SIGNAL. In this case single-ended error
voltage V.sub.EI is a continuous value among a range of values, and
digital converter 1500 provides a multiple bit DIGITAL ERROR SIGNAL
to represent error voltage V.sub.EI.
[0072] FIG. 16 illustrates in partial block diagram and partial
schematic form a third digital converter circuit 1600 that may be
used in current regulated circuit 200 of FIG. 2. Digital converter
circuit 1600 includes a comparator 1610 and a resistor 1620.
Comparator 1610 has a non-inverting input connected to a node that
receives an error current labeled "I.sub.ERROR", an inverting input
connected to ground, and an output for providing a single-bit
DIGITAL ERROR SIGNAL. Resistor 1620 has a first terminal connected
to the non-inverting input of comparator 1610, and a second
terminal connected to the inverting input of comparator 1610 and to
ground (or to any reference voltage). In digital converter circuit
1600, comparator 1610 senses a differential error signal formed by
the voltage drop across resistor 1620 when conducting current
I.sub.ERROR. As before, a control circuit such as a DSP can either
filter and process the single bit signal, or decimate the sequence
of bits over a certain period of time to form a multi-bit digital
code and filter and process the multi-bit digital code.
[0073] FIG. 17 illustrates in partial block diagram and partial
schematic form a fourth digital converter circuit 1700 that may be
used in current regulated circuit 200 of FIG. 2. Digital converter
circuit 1700 includes an ADC 1710 and a resistor 1720. ADC 1710 has
an input connected to a node that receives I ERROR, and an output
for providing a multiple-bit DIGITAL ERROR SIGNAL. Resistor 1720
has a first terminal connected to the node that receives
I.sub.ERROR, and a second terminal connected to ground (or to any
reference voltage). In this circuit resistor 1720 converts
I.sub.ERROR into a voltage, and digital converter 1700 provides a
multiple bit DIGITAL ERROR SIGNAL to represent this voltage.
[0074] In each of these digital converter circuits, the error
signal is level shifted from the floating domain of the sense
resistor into the current regulation and measurement domain. These
circuits do not require accurate gain when performing the level
shifting. Moreover they use either a simple comparator or a
low-cost ADC with a few bits, which is sufficient for high accuracy
current regulation. Note that the comparators used in digital
converter circuit 1400 and 1600 can be used to implement a
successive approximation ADC in which the reference voltages are
changed to search for the digital code that most accurately
represents the input voltage.
[0075] FIG. 18 illustrates in schematic form a sense transistor
1800 that can be used in any of the current regulated circuits of
FIGS. 4, 6, 12, and 13. Sense transistor 1800 is similar to the
previously described sense transistors except that it additionally
has a sense source terminal. Sense transistor 1810 is a composite
N-channel MOS power transistor having a drain terminal labeled "D",
a sense drain terminal labeled "SD", a gate terminal labeled "G", a
source labeled "S", and a sense source labeled "SS". Sense
transistor 1800 is formed using a current conduction element 1810,
a drain sense element 1820, and a source sense element 1830.
Current conduction element 1810 has a drain forming the drain
terminal of sense transistor 1800, a gate connected to the gate
terminal of sense transistor 1800, and a source connected to the
source terminal of sense transistor 1800. Drain sense element 1820
has a drain forming the sense drain terminal of sense transistor
1800, a gate connected to the gate terminal of sense transistor
1800, and a source connected to the source terminal of sense
transistor 1800. Source sense element 1830 has a drain connected to
drain terminal of sense transistor 1800, a gate connected to the
gate terminal of sense transistor 1800, and a source providing the
sense source terminal of sense transistor 1800.
[0076] When operated in the forward direction, positive current
flows from the sense drain to source and the sense source terminal
SS is the reference terminal. When operated in the reverse
direction, positive current flows from the sense source to source
and the sense drain terminal SD is the reference terminal. Sense
transistor 1800 allows the bulk connection of each transistor to be
isolated from the source and is conveniently implemented using an
epitaxial MOS process. Thus sense transistor 1800 provides
additional flexibility in floating ground applications such as the
solenoid with a sense resistor as described in FIG. 2 and similar
FIGs. above.
[0077] While particular embodiments have been described, various
modifications to these embodiments will be apparent to those
skilled in the art. For example, the circuits of FIGS. 2, 3, 4, 12,
and 13 show transistors 232, 332, 436, 1236, and 1352 controlled by
respective control circuits, but in other embodiments the
transistors could be replaced by diodes connected as shown for
diode 150 in FIG. 1. Moreover in other embodiments the topologies
of the circuits shown in FIGS. 2, 3, 4, 12, and 13 above could be
reversed. For example to reverse the topology of current regulated
circuit 200, transistor 230 would be connected between V.sub.BAT
and the first terminal of current sense element 222, and solenoid
210 would be connected between the second terminal of current sense
element 222 and ground.
[0078] Accordingly, it is intended by the appended claims to cover
all modifications of the disclosed embodiments that fall within the
scope of the disclosed embodiments.
* * * * *